1. Field of the Invention
The present invention relates to an isolator that transmits a high-frequency signal in only a specific direction.
2. Description of the Related Art
An isolator that has an unbalanced input port and an unbalanced output port includes a core isolator. The core isolator includes, for example, a first central conductor that connects an input port and an output port to each other, a second central conductor that connects the input port and a ground port to each other, a soft magnetic material core that is provided on a surface thereof with the first central conductor and the second central conductor so as to cross each other while being insulated from each other, and a permanent magnet that applies magnetic flux to a portion where the first central conductor and the second central conductor cross each other.
The isolator needs to be provided with a plurality of impedance elements in addition to the core isolator, and the core isolator is mounted on a circuit board provided with the plurality of impedance elements. As the impedance elements, which constitute the isolator in addition to the core isolator, for example, a capacitor that is connected between the input port and the output port of the core isolator, a resistor that is connected between the input port and the output port of the core isolator, a capacitor and an inductor forming an LC series circuit that is connected between the input port and the output port of the core isolator along with the resistor, and an impedance-adjusting capacitor that is connected between the input port or the output port of the core isolator and an external connection terminal are provided (for example, refer to Japanese Unexamined Patent Application Publication No. 2011-13756).
Conventionally, the plurality of impedance elements of such an isolator are formed separately as chip components. Since arrangement gaps of a certain size or more are provided between the plurality of chip components mounted on a main substrate, if there is a large number of such chip components, in addition to the main substrate becoming larger, connection wiring lines that connect the individual chip components to each other become longer and parasitic components generated by the connection wiring lines cause various problems to arise. For example, a frequency band (isolation band) in which propagation of a signal from the output port to the input port of the isolator is suppressed becomes narrower as a result of a parasitic inductance becoming larger. In addition, passage loss of a signal in the isolator becomes larger as a result of a parasitic resistance becoming larger. Furthermore, the input impedance of the isolator becomes higher as a result of the parasitic inductance and parasitic capacitance becoming larger.